1. Field of the Invention
The present invention relates to a high-frequency circuit device, a resonator, a filter, a duplexer, and a high-frequency circuit apparatus in a microwave band or a millimeter band, used for radio communication and transmission/reception of electromagnetic waves.
2. Description of the Related Art
As a resonator having an electrode film formed on a dielectric substrate, a resonator of a short-circuit circular TM010 mode shown in FIG. 19 and a resonator of a coaxial TEM mode shown in FIG. 20 have been used.
FIG. 19 shows the short-circuit circular TM010 mode resonator viewed from the top, and a cross-sectional view taken along the line A—A thereof. In this example, an electrode 20 is formed on the outer surface of a column-shaped substrate 1. This resonator operates as a short-circuit circular TM010 mode resonator in which the side surface of the column serves as a short-circuit surface.
Also, FIG. 20 shows the coaxial TEM mode resonator viewed from the top, and a cross-sectional view taken along the line B—B thereof. In this example, the electrode 20 is formed on the surface of a cylindrical substrate 1, except the upper surface. With this arrangement, this resonator operates as a coaxial TEM mode resonator which resonates at ¼ wavelength of a used frequency.
A technique of forming a thin-film multilayered electrode, in which a conductive thin-film and a dielectric thin-film are alternately laminated, has been known. With this technique, conductive loss in an electrode formed on the substrate surface can be suppressed. When this technique is applied to a resonator having the configuration shown in FIG. 19 or 20, however, the resonator has an increased loss characteristic. FIG. 21 shows an enlarged view of the circled portion of these figures. In FIG. 21, reference numeral 2 denotes a conductive film and reference numeral 3 denotes a dielectric film.
The known resonator is compact and has a high Q. However, with the demand for miniaturization of high-frequency circuit apparatuses to which these resonators are applied, high-frequency circuit devices such as these resonators are required to be miniaturized, while maintaining a low-loss characteristic.